Patent GB-1351778-A (GB)
Title: Sealing apparatus
IPC: B29C53/40
Filed: 1971-07-23
Abstract: 1351778 Seaming non-metallic sheet material FLUORODYNAMICS Inc 23 July 1971 [24 July 1970] 34782/71 Heading B5K Apparatus for heat sealing thermoplastic film layers 43, 44 comprises clamping members 21, 34 each having a respective clamping surface for receiving the layers 43, 44 therebetween, the member 34 comprising an elongate rigid element 35, means 41, 41a for applying clamping force to the element 35 at a plurality of spaced locations and an elongate fluid-inflatable pressure distributing element 39 interposed between the element 35 and a flexible element 40 for transmitting clamping pressure from the element 35 to a clamping surface, and a narrow elongate heating element 27 extending longitudinally along one of the members 21, 34 adjacent the clamping surface thereof. In one embodiment, Figs. 2-5, the member 21 comprises a plate 22 of magnetic material and having a dove-tailed recess therein with a heat insulating inlay 23. A ribbon-like heating element 27 is supported on the inlay 23 which may be recessed slightly to receive this element. The element 27 may be a nickel-chromium alloy or a nickel-iron alloy and, at one end, is secured to a spring-mounted clamp 28, Fig. 3, and, at the other end, is engaged by a movable clamp 29, Fig. 2, attached to a tensioning cable 30 passing around a sheave 31 connected to a fluid actuator 32 to tension the cable 30 as and when desired. Preferably, a polyimide film 33b, Fig. 5, overlies the element 27 and a nickel-iron alloy foil 33a overlies the film 33b. The element 35 of the member 34 comprises a rectangular-section beam to which a clamping element 36 is loosely connected by bars 36a having limited sliding movement in guides 36b. The element 39 comprises a tube of fabric re-inforced rubber or neoprene. The element 36 includes a channel 37 receiving a heat insulating inlay 38 having a resilient silicone rubber pad 40 secured thereto. A polyimide film 40a is adhered to the pad 40. Fluid actuators 41 act on the beam 35 along the length thereof and at least some of these actuators 41a are of the double-acting type so as to be retractable, the remaining actuators 41 exerting downward pressure on the beam 35 and being retractable by the double-acting actuators. The apparatus may be used to join together overlapping edges of a fluorinated ethylene polymer film to form a tube, e.g. a roller covering or a pipe liner. Holding units 26 which may be mechanical units, electromagnets or permanent magnets are provided to assist in aligning the film edges. In an alternative embodiment, Fig. 6, for sealing heavy gauge films 109, 110 both clamping members have heating ribbons. The lower member 101 comprises a plate 102 with a heatinsulating insert 103, a polyimide film layer 104, a nickel-chromium heating ribbon 105, polyimide film layers 106, 107 and a nickel-iron alloy foil 108. The upper member 111 includes flexible channel 112 having a heat-insulating insert 113, a polyimide film layer 114, a nickel-chromium alloy heating ribbon 115, polyimide film layers 116, 117, a nickel-iron alloy foil layer 118 and a polyimide film layer 119. In a further embodiment, Figs. 7, 11, for in situ installation of coverings of large rolls, e.g. paper machine dryer rolls, the lower clamping member 50 comprises a number of segments assembled to extend fully along the length of the roll 56 to be covered. Each segment comprises a base-plate 54 supported by a resilient pad 55, spacer bars 57, 58, cover plate 59, 60, a heatinsulating inlay 62, one or more polyimide film layers 70, a nickel-chromium alloy heating ribbon 66, one or more polyimide layers 71 and nickel-iron alloy foil layer 72. The ribbon 66 is secured at one end to a gripper 65 and at the other end to a movable gripper 67 carried by fluid actuators 68, 69 to apply tension. The member 50 is secured to the roll 56 by C-clamps 74. The upper clamping member 75 comprises a beam 76 carrying a channel 77 housing a pneumatically inflatable elastomeric tube 78 bearing on a channel 80 containing a heat-insulating inlay 81. A resilient silicone rubber pad 82 and a polyimide film layer 83 are provided. Cross-bars 85 are provided at spaced locations along the beam 76 and carry bolts 87 for the attachment of turnbuckles 88 which engage chains 89 extending around the roll 56. The chains 89 are covered with protective padding 90 where they contact the roll 56 or its covering. Specified thermoplastic films which may be joined by the apparatus are fluorinated ethylene polymers, polyvinylidene fluoride, high molecular weight polyethylene, polypropylene and nylon.